Removed private method of QWinTimeZonePrivate in favor of a local
static that returns a rule index rather than a rule; this prepares the
way for smarter searching in transition-finding methods. In the
process, re-work the function to use binary chop instead of a linear
search through a potentially long sorted list.
Change-Id: I2171e3f01afa3037b9718e1be7d0c9343aa74ff0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>